The present invention relates to a sealing structure for use with a rotary heat-regenerative heat exchanger.
FIG. 1 of the accompanying drawings shows the general structure of a prior art rotary regenerative heat exchanger, which may, for example, be utilized in a gas turbine. Reference numeral 1 denotes a housing in which a compressed air passage 2 for conducting compressed air is formed. This compressed air is compressed in a compressor 20, and flows through the passage 2 into a combustor 21, after being heated by the regenerator 4, which is explained in more detail later. Fuel is injected into the stream of compressed air in the combustor 21, and the mixture is ignited. Accordingly, its temperature and pressure rise to high levels. The combustion gases thus produced exhaust, at high speed, temperature, and pressure, through a compressor turbine 22 which rotates the compressor 20, and thence pass to a power turbine 23 to produce output power for external use. From the power turbine 23, these gases pass into the combustion gas passage 3 in the housing 1. After flowing through the regenerator 4, these combustion gases are discharged.
The regenerator 4 is formed as a cylindrical member which crosses over both passages 2 and 3, and which rotates around its central axis while maintaining mutual isolation of these passages 2 and 3. Thereby, heat is transferred from the hot combustion gases flowing through the passage 3 to the cold compressed air flowing through the passage 2, thereby increasing the temperature of the compressed air fed into the combustor 21, thus improving efficiency of the turbine, and also reducing the temperature of the exhausted combustion gases, thereby reducing the difficulty of disposing of them, and reducing thermal pollution of the environment.
In such a turbine, the structure of the regenerator 4 is such that gases can only, substantially, flow through it in its axial direction, and thereby gases are prevented from crossing between the passages 2 and 3, which tends to occur because the gas pressure is generally higher in the passage 2, which contains compressed air, than in the passage 3, which contains exhausted combustion gases. Thus, sealing elements must be provided to prevent transfer of gases between the passages 2 and 3 around the sides of the regenerator 4.
In FIG. 1, such sealing elements are shown as provided between the passage 3 and the regenerator 4. The upstream sealing element 5 is on the hot side of the regenerator 4, and the downstream sealing element 6 is on the cool side of the regenerator 4, in the passage 3.
The details of construction of such a prior art sealing device are shown in FIG. 2. This sealing structure has already been proposed by us for improving upon conventional sealing performance by using the pressure difference between the two passages 2 and 3. In this figure, as in all subsequent figures of this application, the structure shown is a partial section through a sealing device, and it is preferable that this sealing device is circularly symmetrical about the central axis of the circular passage 3, i.e., about an axis approximately shown in FIG. 1 by the arrow pointing downwards in the lower part of passage 3. It is arranged that a toroidal space 9, around the regenerator 4, is communicated with the high pressure compressed air in the passage 2, upstream of the regenerator 4. As explained above, this compressed air is at substantially higher pressure than the gases in the passage 3. Seal elements 5 and 6, supported by seal holders 10, are disposed on the upper and the lower sides of the regenerator 4. On the back of the lower seal holder 10 is attached, by a plurality of bolts 13, a seat member 12 formed of a heat resistant elastic material such as silicon rubber. A pressing plate 14 is fixed to the housing 1, in the location shown, by a spacer 11, a plurality of bolts 16, and a retainer plate 15. The free circular edge of the plate 14 is in pressing contact with a projecting circular ring on the seat member 12. The arrangement described above is circularly symmetric, so that the spacer 11, the pressing plate 14, the retainer plate 15, the seat member 12, the seal elements 5 and 6, the seal holders 10, etc., are all toroidal. A plurality of studs 17 are screwed through the housing 1 to abut against the base portion 12a of the seat member 12, so as to compress the seal elements 5 and 6 with a predetermined pressing force, during the assembly of the structure, so as to prevent the pressing plate 14 from damage during this assembly.
According to this structure, the higher gas pressure present in the space 9 presses on the back of the pressing plate 14 and presses it against the seat member 12, so as to compress the two seals 5 and 6 against the regenerator 4 and ensure a good seal. Even after substantial wearing of the seals 5 and 6, this pneumatic pressure ensures that good contact and sealing tends to be maintained. According, thus, to this prior art device, the resilience of the pressing plate 14 is not entirely relied upon for the pressing of the seals 5 and 6 against the regenerator 4.
However, the above described structure is not completely satisfactory. As the seal elements 5 and 6 wear away, much alteration in shape is required from the pressing plate 14, which sometimes cannot cope with the amount of movement required. When this occurs, there is a tendency for a gap to open up between the pressing plate 14 and the seat member 12, especially when the pressure in the space 9 is low, as during starting of the gas turbine. Thereby, poor sealing may occur.
Another problem may occur, in that, because the seat member 12 is made of silicon rubber or the like, its heat resistance is not as good as that of metal.